The field of this invention is analyte determination.
Analyte detection in physiological fluids, e.g., blood or blood derived products, interstitial fluid, etc., is of ever increasing importance to today""s society. Analyte detection assays find use in a variety of applications, including clinical laboratory testing, home testing, etc., where the results of such testing play a prominent role in diagnosis and management in a variety of disease conditions. Analytes of interest include glucose for diabetes management, cholesterol, and the like. In response to this growing importance of analyte detection, a variety of analyte detection protocols and devices for both clinical and home use have been developed.
Historically, blood glucose and other bodily analyte measurements were invasive. Such measurements were generally made by withdrawing a blood sample and measuring the desired analyte within the blood or plasma. Blood samples were typically withdrawn by inserting a needle into a major artery or, more commonly, a vein. Such direct vascular blood sampling employed by these early methods had several limitations, including pain, hematoma and other bleeding complications, and infection. In addition, due to the vascular damage resulting from the needle puncture, sampling could not be repeated on a routine basis. Finally, it was extremely difficult for patients to perform a direct vascular puncture on themselves.
A more recent technique that has been developed to overcome some of the disadvantages associated with the above protocols is to collect a blood sample by cutting or lancing the skin and the subcutaneous tissue, including the small, underlying blood vessels, to produce a localized bleeding on the body surface. A lancet, knife, or other cutting device is required. The blood on the body surface is then collected into a small tube or other container. The fingertip is the most frequently used site to collect blood in this method due to the large number of small blood vessels located in the region. One method is shown in U.S. Pat. No. 4,637,403. This sampling method also suffers from several major disadvantages, including pain and the potential for infection and other problems associated with repeated sampling for a confined area. Pain is a major disadvantage since the fingertip has a large concentration of nerve endings. Also, there is a limited body surface area from which to take these samples and measurement on a high frequency basis.
Because the above described prior art invasive techniques are painful, patients frequently avoid having blood glucose measured. For diabetics, the failure to measure blood glucose on a prescribed basis can be very dangerous. Also, the invasive techniques, which result in lancing blood vessels, create an enhanced risk for disease transmission.
Attempts have been made to develop glucose and other analyte sensors for implantation in the human body. Advantages of such implanted sensors include the ability to provide xe2x80x9ccontinuous,xe2x80x9d chronic monitoring without having to consciously sample blood at each measuring event. Despite the many potential advantages provided by implanted sensors, development of a permanently implanted or long-term, chronic implanted sensor has been unsuccessful. Attempts to develop short-term implantable sensors (up to 2-3 days) have also met with very limited success. Most implantable sensors are based on measuring various products from chemical reactions between agent(s) located on or within the sensor and the desired analyte. Implanted glucose sensors have typically used the glucose oxidase reaction to measure the amount of glucose, as described in U.S. Pat. No. 5,108,819. Such implantable glucose sensors have been intended for insertion through the epidermis and dermis to the subcutaneous tissue. An alternative location previously described for chronic sensor implant is the peritoneal cavity. Implanted sensors typically require direct or telemetered connection to a measurement instrument, usually located external the body.
All implanted sensors are faced with several major problems. First, all foreign materials, including materials incorporated into a glucose sensor, produce unwanted body reactions. Such reactions include the formation of fibrotic tissue around the sensor which alters the sensor""s contact with normal body fluids and analytes, such as glucose. The body""s natural defense mechanism may also have a direct xe2x80x9cpoisoningxe2x80x9d effect upon the sensor""s operation by interfering with the chemical reactions required by chemical-based sensors. As with any implanted object, implanted sensors may also initiate other bodily reactions including inflammation, pain, tissue necrosis, infection, and other unwanted reactions.
Implanted sensors require certain chemicals and chemical reactions to determine the level of analyte in the surrounding medium. These chemical reactions are the source of the other major problem facing any implantable sensor. Chemically-based sensors require products to be consumed and other products to be produced as part of the sensor""s normal operations. Therefore, the sensors can quickly be depleted of the chemical agents required to sustain the desired chemical reactions. Secondly, by-products are given off as a result of the basic chemical reaction. These by-products often xe2x80x9cpoisonxe2x80x9d the sensor or cause other unwanted tissue reactivity. Because of these severe limitations, implanted sensors are not practical. Finally, such implanted sensors are painful to implant and are a source of infection.
As such, while offering benefits over traditional analyte measurement devices and protocols, such as continual, automated monitoring of the analyte of interest, implantable analyte concentration measurement devices currently available are unsatisfactory for a number of reasons.
Accordingly, there is a continued interest in the development of new analyte concentration measurement protocols and devices. Of particular interest would be the development of a continuous analyte concentration measurement system that does not suffer from disadvantages experienced with implantable sensors, as reviewed above.
U.S. Patents of interest include: U.S. Pat. Nos. 4,680,628; 4,721,677; 5,002,054; 5,108,819; 5,161,532; 5,390,671, 5,582,184; 5,682,233; 5,746,217; 5.820,570; 5,879,310; 6,056,738; 6,086,545; 6,091,975; and 6,155,992.
In accordance with the present invention there is provided a method for determining the analyte concentration in a host over a period of time. The method comprising the steps of: (a) making a first analyte concentration measurement at a first point of time using a single use analyte concentration measuring device; (b) making a second analyte concentration measurement at a second point in time using a single use analyte concentration measuring device; and (c) making one or more additional analyte concentration measurements using another single use measuring device, wherein the analyte concentration measurements are made according to a selected schedule to monitor the concentration of analyte in a host over a given portion of time.
In accordance with the present invention there is provided a method of monitoring the concentration of glucose in interstitial fluid of a host over a given period of time. The method comprising the steps of: (a) making a first interstitial fluid glucose concentration measurement at a first point in a time period using a single use interstitial fluid glucose concentration measurement device; (b) making a second interstitial fluid glucose concentration measurement at a second point in the time period using a single use interstitial fluid glucose concentration measurement device; and (c) making one or more additional interstitial fluid glucose concentration measurements according to a predetermined schedule to monitor the concentration of glucose over a period of time.
In accordance with the present invention there is provided a system for use in monitoring the concentration of analyte in a host over a portion of time, the system comprising a removable cartridge, the cartridge includes at lease a first and second single use analyte concentration measuring devices. The system further includes a device into which the cartridge may be inserted, wherein the device includes an activation means for selectively activating the first and second measurement devices of the cartridge according to a predetermined schedule.
In accordance with the present invention there is provided a kit for use in monitoring the concentration of an analyte in a host over a given period of time. The kit includes a removable cartridge; the cartridge includes at lease a first and second single use analyte concentration measuring devices. The system further includes a device into which the cartridge may be inserted, wherein the device includes an activation means for selectively activating the first and second measurement devices of the cartridge according to a predetermined schedule.